The present invention relates in general to air conditioning apparatus including associated energy storing systems, and more particularly to an improved apparatus for storing ice or eutectic material (hereinafter sometimes referred to as "negative heat energy storage material"), for supply of stored negative energy during peak electrical demand times, while sequentially providing at a different time period direct air conditioning without circulating the refrigerant liquid into the tank for storing the ice or eutectic material, thereby to avoid unnecessary melting and consequently the necessity for refreezing of the negative heat energy storage material.
In the prior art, certain combined air conditioning apparatus with associated negative energy storage systems have been developed for the purpose of efficiently exploiting the two-tier pricing system utilized by electrical utilities. In particular, one such exemplary apparatus is set forth in U.S. Pat. No. 4,735,064 to Fischer.
By way of background, electrical utilities have developed a two-tier pricing structure which is divided into peak hours and off-peak hours. Peak hours occur when electrical demand is maximized, such as those periods of the day corresponding to the average daily highest temperatures, and which generally relate to some extent to those hours surrounding the afternoon-time period. One important reason for the relatively high extent of electrical demand during the period of the day when the temperatures are the greatest (i.e., at the "peak hours") is because of the utilization of air conditioning systems in a large percentage of commercial and residential buildings. The "off peak" hours occur when electrical demand is minimized. The "off peak" hours correspond generally to the time period around and after the midnight hour, when the demand for cooling, if any, is minimized because of the relative inactivity of persons, and when the utilization of electricity for electrical lighting is likewise minimized for the same reasons.
As a result of the greater demand for electricity during the peak hours of the day, the rate prices for electricity during such peak hours are substantially greater than the rate prices for electricity during the off peak hours.
The amount of electricity utilized at business and residential buildings is substantial during peak hours. In view thereof, it has been proposed (such as for example in U.S. Pat. No. 4,735,064 to Fischer) that it would be optimally advantageous to utilize electrical devices, such as air conditioning compressors, only during off peak times, and to utilize stored energy during the peak times.
These prior art structures are directed to apparatus having a storage tank which is built around cooling coils. The coils contain a refrigerant. A condensing unit is connected to the coils for supplying liquid refrigerant to the coils, which upon expansion freeze or solidify the material in the tank during a first time period which corresponds to the period of off peak electrical demand. The coils are also connected to an evaporating unit which receives cold refrigerant liquid from the coils during a second time period which corresponds to the period of peak electrical demand. In addition, the condensing unit is typically connected to the evaporator unit by means of conduits passing through the tank, and thus for providing refrigerant to the evaporating unit during a third time period, when some cooling may be necessary. This third time period occurs during off peak hours. Energy use and operating cost are reduced by operating to provide cooling in this way during off peak hours.
There have been certain defects and disadvantages associated with these prior art structures and methods. For example, one problem in particular is that there is melting of some of the ice in the tank when the system is operated during the third time period. Yet further, operation has proved to be less than optimally efficient due to low evaporating temperature in the cooling mode and due to low evaporating temperature operation in the ice making mode to re-make the ice which has been melted during the cooling mode operation. Thus, there is an "energy penalty" associated with cooling by the freezing and melting of ice as compared to conventional air conditioning methods involving direct through pumping of refrigerant from a condensing unit to an evaporating unit.
In view of the defects and deficiencies associated with prior art systems, it is an object of the present invention to provide an improved combined multi-modal air conditioning apparatus and negative energy storage system which permits optimally efficient operation by means of by-passing of the tank by the circulating refrigerant when the apparatus is in the direct-cooling mode, thereby to avoid melting the stored negative heat energy storage material, usually comprising ice, which then does not have to be refrozen.
It is another and further material object of the present invention to provide a multi-modal air conditioning apparatus and energy storing system which has improved operating cost efficiency over prior art systems. It is another and further material object of the present invention to provide a multi-modal air conditioning apparatus and energy storing system which, by virtue of the method of by-passing of the tank by the circulating refrigerant, can also be operated as a conventional heat pumping system also. Other objects and advantages of the present invention will be made more apparent hereafter.